Antihalation layer for photographic sensitive materials



- PATENT OFFICE ANTIBALATION LAYER non rno'ro- GRAPHIC SENSITIVE MATERIALS Olaf Frederick Bloch, Ilford, England, assignor to Ilford Limited, Ilford, Essex, England, a British company .No Drawing. Application July 2c, 1938, Serial No. 221,395. In Great Britain July 21. 1937 13 Claims.

This invention comprises improvements in antihalation layers for photographic sensitive materials more particularly for those comprising silver halides and intended to be developed by the reversal process.

In the reversal process the silver halide photographic material is exposed and the latent image developed to yield 'a metallic silver image which is then removed by treatment in a silver solvent which does not affect undeveloped silver halide and thereafter the unaffected residual light-sensitivematerial is exposed and developed to produce the final image corresponding to the original subject.

This invention relates particularly to the provision of means for reducing or eliminating halation effects which may be produced during the first exposure.

It has already been proposed to avoid halation eflects by the use of dyed layers of material such as gelatin, applied to the rear surface of the support of photographic material or as an intermediate layer between the support and the pho tographic emulsion.

It has also been proposed to employ antihalation layers of suitable material, for example, gelatin containing suspended colloidal silver or manganese dioxide in various-forms.

The use of dyed layers is open to the almost insuperable objection that the choice of dyes must be limited to those having no deleterious effect on the photographic emulsion with which the anti-halation layer may come into contact either -directly when used as a-layer adjacent to the emulsion layer or by contact during storage when the layer is applied to the rear surface of the support and that all the dyes having these rare characteristics, when used in concentration sufficient to produce the desired reduction in halation, are

incapable of complete removal but give rise to' staining and colouring of the film which is very undesirable when the final image is on the original film, as in the reversal process.

The manganese dioxide layers also suffer from a the disadvantage that they usually impair the keeping qualities of the unexposed films and are difiicult to remove completely.

I have now found that finely divided or colloidal silver sulphide suspended in a suitable medium forms a very useful material which can be employed for reducing halation effects either in the form of an intermediate layer between the support and the emulsion or as a backing layer on the rear surface of the emulsion support or again as a super coat on the emulsion when the material is intended to be exposed through the support.

Such material has the advantage of having no effect upon the sensitive emulsion-and the silver sulphide can be removed completely by treatment in the acid permanganate reversal bath frequently used for removal of the first .developed silver image.

' The invention accordingly consists in lightsensitive photographic material for use in the reversal process including an anti-halation layer comprising finely divided silver sulphide particles suspended in a water permeable binding a ent.

Preferably the silver sulphide particles are of colloidal dimensions but they may include or consist of particles of larger size which are capa-' ble of remaining in suspension in the binding agent and which may be measurable under a microscope.

The binding agent must, of course, be permeable to the bath used for the removal of the silver sulphide and, when applied as a super coat, also to the photographic developing baths and may consist, for example, of gelatin, casein, water permeable synthetic resins or the like.

The invention also provides the method of preparing light-sensitive photographic material having an anti-halation layer as described above which includes the steps of preparing a mixture of gelatin or other suitable binding agent and silver nitrate, converting part but preferably not the whole of the silver nitrate to silver sulphide by treatment with a water-soluble, sulphide, washing the soluble salts out of 'the mixture and then coating the silver sulphide suspension so formed -on to a support or on to a light sensitive layer of silver nitrate in this manner ensures that no soluble sulphides are present in the anti-halation layer while the silver'hallde arising from the conversion of the excesssilver nitrate is removed during the normal fixing operation together with the unused silver halide of the photographic emulsion.

One example of a method'of preparing material according to the invention for use as antihalation layers is as follows. Five grams of gelatin are dissolved in 150 ccs. of water at a temperature of 125? F. and to this is added, with continuous stirring, a cool solution of 1'7 grams of silver nitrate in distilled water to make up 40 cos. A solution of 12 grams sodium sulphide crystals (Na-is 9HzQ) and 10 cos. of ammonia (S. G. 0.920) with water to make up 160 ccs. is then added to the above mixture again with continuous stirring. A further solution of 1.16

the anti-halation layer.

grams sodium chloride and water to make up 23 ccs. is then added to the mixture with stirring.

The product so obtained is then filtered through swansdown into a solution of grams gelatin in 200 cos. of water at 125 F. The resulting mixture is allowed to set, is shredded, and is then thoroughly washed in eight or more changes of water. It is then melted and has added to it 30 ccs. of a 6% alcoholic solution of phenol. The resulting material is an emulsion of colloidal silver sulphide in gelatin and after filtering the emulsion is used to produce an anti-halation layer by coating on a film base in the usual way and to give a transmission density of approximately 1.0. A normal panchromatic reversal emulsion is then coated over the anti-halation layer.

'It is found that the silver sulphide in the antihalation layer is completely removed by a normal reversal bleaching bath containing acidified potassium permanganate (KMnO4).

It is to be understood thatwhen the material according to the invention is used in the reversal process it is desirable that a potassium permanganate'bleaching bath be used for the removal ofthe original silver image rather than a bichromate bleaching bath which has been found unsuitable for removing the silver sulphide from Anti-halation layers prepared as described above'ha ve been found to have particularly good anti-halation properties and to'have little or no light sensitigellayer.

I claim:

1. Light-sensitive photographic material for use in the reversal process including an antihalation layer comprising finely divided silver sulphide particles suspended in a water permeable binding agent.

2. Light-sensitive photographic material for use in the reversal process including an antihalation layer comprising finely divided silver sulphide particles suspended in a binding agent taken from the group gelatin, casein and water permeable synthetic resins.

3. Light-sensitive photographic material for use in the reversal process including an anti-halation layer comprising finely divided silver sulphide particles suspended in gelatin.

4. Lightsensitive photographic material comprising a support and, carried on the support, a light-sensitive layer and an anti-halation layer comprising finely divided silver sulphide particles suspended in a water permeable binding agent.

5. Light-sensitive photographic material comprising a support, a light-sensitive layer carried on the support and between the support and the light-sensitive layer an anti-halation layer comprising finely divided silver sulphide particles suspended in a water permeable binding agent.

. 'efie'ct on the normal keeping properties'of the 6.Light-sensitivephotographic material comprising a support, a light-sensitive layer on one 'side of the support and as a backing on the other side of the support an anti-halation'layer comprising finely divided silver sulphide particles suspended in a water permeable binding agent.

7. Light-sensitive photographic material comprising a support, a light-sensitive layer carried on the support and, as a super coat on the lightsensitive layer, an anti-halation layer comprisa photographic element to ing finely divided silver sulphide particles suspended in a water permeable binding agent.

8. The method of preparing light sensitive photographic material having an anti-halation layer which includes the steps of preparing a 5 mixture of a water permeable binding agent and silver nitrate, treating said mixture with a water soluble sulfide in an amount stoichiometrically insufiicient to convert the silver nitrate to silver sulfide, setting the mixture, washing out the soluble salts and then coating the silver sulfide suspension thus formed onto a photographic element to form an anti-halation layer.

9. The method of preparing light sensitive photographic material having an anti-halation layer which includes the steps of preparing a mixture of a water permeable binding agent and silver nitrate, treating said mixture with a water soluble sulfide in .an amount insufficient to convert all of said silver nitrate to silver sulfide, setting the mixture, washing out the soluble salts and then coating the silver sulfide suspension so formed onto a light sensitive layer carried on a support, thereby to form an anti-halation layer.

10. The method of preparing light sensitive photographic material having an anti-halation layer which includes the steps of preparing a mixture of gelatin and silver nitrate, treating said mixture with a water soluble sulfide in an amount sufiicient to convert only a part of the silver nitrate to silver sulfide, setting the mixture, washing out the soluble salts and then coat-. ing the silver sulfide suspension thus formed onto form ananti-hala-' 35 tion layer.

11. The method of preparing 1igh t sensitiVe photographic materials having an anti' halation layer which includes the steps of. preparing a mixture of gelatin and silver nitrate, treating said mixture with a water soluble salt in an amount suflicient to convert only a part of the silver nitrate to silver sulfide, setting the mixture, washing out the soluble salts and then' coating the silver sulfide suspension thus foimed onto a light sensitive layer carried on a support to form, an anti-halation layer.

12. The method of preparing a light sensitive photographic material having an anti-halation layer which includes the steps of preparing a mixture of a water permeable binding agent and silver nitrate, converting only a portion of the silver nitrate to silver sulfide by treatment with a water soluble sulfide, converting the remainder of the silver nitrate to silver halide, setting the coating the suspension of silver sulfide and silver halide so formed onto a support to form the anti-halation layer.

13. The method of preparing a light sensitive photographic material having an anti-halation layer which includes the steps of preparing a mixtureof a water permeable binding agent and silver nitrate, converting only a portion of the silver nitrate to silver sulfide by treatment with a water soluble sulfide, converting the remainder of the silver nitrate to silver halide, setting the mixture, washing out the soluble salts and then coating the suspension of silver sulfide and halide so formed on to a light sensitive layer carried 7 on a support to form the anti-halation layer.

OLAF FREDERICK BLOCH. 

